Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model

While the Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down under anthropogenic warming, the exact role of the AMOC in future climate change has not been fully quantified. Here, we present a method to stabilize the AMOC intensity in anthropogenic warming experiments by removing fresh water from the subpolar North Atlantic. This method enables us to isolate the AMOC climatic impacts in experiments with a full-physics climate model. Our results show that a weakened AMOC can explain ocean cooling south of Greenland that resembles the North Atlantic warming hole and a reduced Arctic sea ice loss in all seasons with a delay of about 6 years in the emergence of an ice-free Arctic in boreal summer. In the troposphere, a weakened AMOC causes an anomalous cooling band stretching from the lower levels in high latitudes to the upper levels in the tropics and displaces the Northern Hemisphere midlatitude jets poleward.

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Observed early-warning signals for a Greenland-ice-sheet tipping point

10.5194/egusphere-egu2020-7369 ◽

2020 ◽

Author(s):

Martin Rypdal ◽

Niklas Boers

Keyword(s):

Early Warning ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Meridional Overturning Circulation ◽

Temperature Threshold ◽

Warning Signals ◽

Early Warning Signals ◽

Current State ◽

Meridional Overturning ◽

Global Sea Level

<p>Nonlinear feedbacks, such as the melt-elevation feedback, may produce a critical temperature threshold beyond which the current state of the Greenland Ice Sheet loses stability. Hence, the ice sheet may exhibit an abrupt transition under ongoing global warming, with substantial impacts on global sea level and the Atlantic Meridional Overturning Circulation. Melting rates across Greenland and solid ice discharge at the ice sheet's margins have recently accelerated. In this work, we analyze ice sheet runoff reconstructions and process-based simulations using new methods. We compare the acceleration in the runoff with the statistical properties of fluctuations around the system's equilibrium. The analysis uncovers significant early-warning signals for an ongoing destabilization and substantial further mass loss in the near future.&#160;</p><p>&#160;</p>

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Decadal windstorm activity in the North Atlantic-European sector and its relationship to the meridional overturning circulation in an ensemble of simulations with a coupled climate model

Climate Dynamics ◽

10.1007/s00382-013-1975-6 ◽

2013 ◽

Vol 43 (5-6) ◽

pp. 1545-1555 ◽

Cited By ~ 7

Author(s):

Katrin M. Nissen ◽

Uwe Ulbrich ◽

Gregor C. Leckebusch ◽

Ivan Kuhnel

Keyword(s):

North Atlantic ◽

Climate Model ◽

Meridional Overturning Circulation ◽

Coupled Climate Model ◽

Overturning Circulation ◽

The North ◽

Meridional Overturning ◽

The North Atlantic ◽

European Sector ◽

Ensemble Of Simulations

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Links between the Southern Annular Mode and the Atlantic Meridional Overturning Circulation in a Climate Model

Journal of Climate ◽

10.1175/2010jcli3576.1 ◽

2011 ◽

Vol 24 (3) ◽

pp. 624-640 ◽

Cited By ~ 14

Author(s):

Camille Marini ◽

Claude Frankignoul ◽

Juliette Mignot

Keyword(s):

Time Scales ◽

North Atlantic ◽

Time Scale ◽

Climate Model ◽

Drake Passage ◽

Atlantic Meridional Overturning Circulation ◽

Southern Annular Mode ◽

Meridional Overturning Circulation ◽

Overturning Circulation ◽

Meridional Overturning

Abstract The links between the atmospheric southern annular mode (SAM), the Southern Ocean, and the Atlantic meridional overturning circulation (AMOC) at interannual to multidecadal time scales are investigated in a 500-yr control integration of the L’Institut Pierre-Simon Laplace Coupled Model, version 4 (IPSL CM4) climate model. The Antarctic Circumpolar Current, as described by its transport through the Drake Passage, is well correlated with the SAM at the yearly time scale, reflecting that an intensification of the westerlies south of 45°S leads to its acceleration. Also in phase with a positive SAM, the global meridional overturning circulation is modified in the Southern Hemisphere, primarily reflecting a forced barotropic response. In the model, the AMOC and the SAM are linked at several time scales. An intensification of the AMOC lags a positive SAM by about 8 yr. This is due to a correlation between the SAM and the atmospheric circulation in the northern North Atlantic that reflects a symmetric ENSO influence on the two hemispheres, as well as an independent, delayed interhemispheric link driven by the SAM. Both effects lead to an intensification of the subpolar gyre and, by salinity advection, increased deep convection and a stronger AMOC. A slower oceanic link between the SAM and the AMOC is found at a multidecadal time scale. Salinity anomalies generated by the SAM enter the South Atlantic from the Drake Passage and, more importantly, the Indian Ocean; they propagate northward, eventually reaching the northern North Atlantic where, for a positive SAM, they decrease the vertical stratification and thus increase the AMOC.

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